Shaped beam tube having fine mesh closely adjacent substantially rectangular trim aperture

ABSTRACT

A shaped beam tube is described wherein a mesh is provided adjacent a trim aperture to diffuse the beam (which is utilized to flood the shaping aperture) and to produce a substantially uniform intensity over the cross section of the beam.

313 -4143 7 0 x9 345796-14 SR K (of [72} Inventor Charies R.Corpew 5 References Cited 119M958, UNITED STATES PATENTS 5 Qff' l g 2.644.906 7/1953 1366616 313/86x [2 l 2,824.250 2/1958 McNaney 6161.... 313/8604) Paemed May 1971 932 6/1960 McNane 313/86 731 Assignec Shmflbflg Daiagraphicslnc. 2939' Y l San). Cam 3,143,681 8/1964 Schlesmger. 313/83 3.151.270 9/1964 Croweli 3l3/83X 3,354,335 11/1967 Corpew... 313/77 2,877,369 3/1959 NiCOH 313/8500 3,049,641 8/1962 GlCiCh3Uf.... 313/8204 \7 3,143,685 8/1964 01 565 313/82(X) 541 SHAPED BEAM TUBE HAv 1:1: FINE MESH CLOSELY ADJACENT SUBSTAN'H ALLY pnmay Bummer-be Sega RECTANGULAR TRXM APERTURE Attorney-Anderson, Luedcka, Fitch, Even and Tabm 5 (Ilaims, 4 Drawing Figs. 521 us.c1 313/86, ABSTRACT: A shaped beam tube is described wherein a 313/77 mesh is provided adjacent a trim aperture to diffuse the beam [51] Int.Cl HHOtj 29/56, (which is utilized to flood the shaping aperture) and to HOlj'29/7OQHOX j 29/06 produce a substantially uniform intensity "overthecross sec- 1 tion of the beam.

field ofSeard! 3l3/86,77

Patented May 18, 1971 24mm SE 5 6 56 d5. 5% It;

:82 Sort; 355. 5&2:

mvsm'ro CHARLES R. CORP 1; ATTYS SHAPED BEAM TUBE HAVING FINE MESH CLOSELY ADJACENT SUBSTANTIALLY RECTANGULAR TRIM APERTURE through which the beam is directed. Beam trimming means 16 defining a trim aperture 17 are positioned between the beam producing means 11 and the beam shaping means 13 for blocking electrons toward the fringe of the beam and thereby reducing the beam cross section. A mesh 18 is positioned adjacent the beam trimming means 16 for dividing the beam to produce a substantially uniform intensity over the cross sec tion of the beam passing through the trim aperture 17.

Referring now more particularly to HO. 1, a shaped mam tube constructed in accordance with the invention is illusshape to the shaped cross section of the beam. Shaped beam tubes of this type have found commercial use in numerous applications for displaying various types of data.

Normally, in shaped beam tubes, the electron beam iS shaped by passing the same through a selected one of a group of stencillilte apertures in an electron opaque plate. The stencillike apertures correspond to characters, such as letters of the alphabet, or to portions of characters, graphs, or mathematical curves. During its course from the cathode of the shaped beam tube to the target screen, the electron beam is deflected to pass through a selected one of the apertures and is then redeflected to a desired position on the target screen.

When a particular shaping aperture is selected, it is prefera ble to avoid passing any part of the electron beam through adjacent apertures, since the quality ofthe display will be adversely affected under such conditions. To avoid this, a trim aperture is generally placed atsome position prior to the shaping aperture. The trim aperture, formed in an electron opaque plate, reduces the cross section of the beam by an amount which leaves only enough beam cross section to satisfactorily illuminate the shaping aperture.

Typically, after passing through a trim aperture, the intensity of an electron beam is strong near its center, but falls off quickly toward its edges. lack of uniformity in intensity may result in poor character quality on the target screen due to excessive variation in brightness between various parts of the displayed character. To avoid this, the shaping apertures may be spaced a sufficient distance from each other that only the central portion, that is, the portion of uniform beam intensity, illuminates the shaping aperture. To avoid illumination of adjacent-apertures, however, aperture spacing must necessarily be sufficiently great. Accordingly, a limitation is placed upon the number of shaping apertures which may be utilized in the available area for a given size of shaped beam tube.

An object of the present invention is to provide an improved shaped beam tube.

Another object of the invention is to provide a shaped beam tube capable of incorporating a large number of shaping apertures for a given available area.

A further object of the invention is to provide a shaped beam tube in which a more uniform beam intensity is attained prior to passing the beam through a shaping aperture.

Other objects of the invention will become apparent from the following description, taken in connection with the accompanying drawings wherein:

HO. 1 is a schematic exploded view, in perspective, of a shaped beam tube constructed in accordance with the inventron",

FIG. 2 is a graph illustrating the improvement in uniformity of beam intensity which is attainable through the invention; and,

FIGS. 3 and 4 are illustrative of one of the improvements attainable through the invention.

Very generally, the shaped beam tube of the invention includes means ll for producing a beam of electrons, and a target screen l2 toward which the beam of electrons is directed and upon which the beam of electrons impinges. Beam shapf g means 13 defining a plurality of apertures 14 are positionod between the beam producing means and the target screen for forming the cross section of electron beam into predetermined shapes depending upon the particular aperture trated schematically. The internal elements of the illustrated tube are enclosed within a glass envelope 19 which may be of any suitable shape. The target screen 12 is disposed upon the inside of a circular glass face plate of the envelope 19. The end of the envelope l9 opposite the target screen is suitably closed and provided with a plurality of pins, not illustrated, passing therethrough to provide for electrical connection to the internal elements of the tube.

The cathode ll which produca the electron beam is generally cup shaped and is heated by a suitable heating filament, not illustrated, disposed within the cup. The outer surface of the cathode 11 may be comprised of nickel coated with barium oxide or some other similar material which produces free electrons at elevated temperatures. Such electrons are accelerated toward the target screen in a beam by various elements which are described subsequently. The cathode is maintained by an appropriate biasing circuit, not shown. at a potential Vl which may be, for example, -2 ltv.

For controlling the overall intensity of the electron beam as it leaves the cathode 11, a cup-shaped grid electrode 2l is positioned over the cathode and has an opening 22 aligned on the axis of the path of the electron beam. The grid electrode 21 is maintained at a potential V2 which is more negative than the cathode potential V1 by an amount dependent upon the desired overall beam intensity. Typical operating conditions may have the voltage V2 about 35 volts more negative than Two cylinders, 23 and 24, are positioned between the cathode 11 and the trim aperture 17. The cylinders 23 and 24 are maintained at potentials V3"and V4, respectively, for establishing an electrostatic-focusing field through which the beam passes. The potentials V3 and V4 are positive with respect to the cathode 11 and cause acceleration of the electron beam toward the trim aperture 17. The beam trimming means 16 which define the trim aperture 17 consist, in the illustrated embodiment, of a hollow circular electron opaque plate 16 positioned within a cylinder 26, both the plate and the cylinder being maintained at or near a suitable potential. which is ground in the illustrated embodiment. The potentials V3, V4 and the potential on the cylinder 26 and plate 16 are such that the cross section of the beam at the trim aperture 17 is larger than the aperture. Assuming the plate in and cylinder 26 to be at ground potential, typical operating potentials for V3 and V4 may be +2 ltv. and l kv., respectively.

Following the trim aperture 17 are two more cylinders 27 and 28. The cylinder 27 is maintained at a potential V5 and the cylinder 28 is maintained at the reference potential. The omration of the cylinders 27 and 23 will be described sub sequently. After passing through the electrostatic fields established by the'cylinders 37 and 28, the bean is deflected to select one of the plurality of apertures'bi in. the beam shaping means or electron opaque plate 13 by means of horizontal deflection plates 29 and vertical deflection plates 31. Suitable potentials applied across the plates by means, not illustrated, cause selection of a desirtxl one of the apertures l4.

The plate 13 in which the apertures 14 are formed is sup ported in a focusing cylinder 32, and the plate 13 and cylinder 32 are maintained at or near ground potential. After selection ofa particular aperture l4, the beam is redirected toward the axis of the tube by an electrostatic lens consisting of the cylinders 52 and 62 together with the cylinder 32. The cylinders 32 and 62 are maintained at ground potential, while the cylinder 52 is operated at a difierent potential V6. The electric fields at the potential discontinuities between the cylinders 32 and S2, and between the cylinders 52 and 62, direct the beam toward the axis in the region between a pair of horizontal deflection plates 33 and a pair of vertical deflection plates 34. A suitable potential for V6 is -2,000 volts. Voltages applied to the pairs of plates 33 and 34 will. complement the initial deflecting voltages applied to the pairs of plates 29 and 31 so that the beam is re rned to the axis of the tube within a deflection yoke 36. The Currents in the deflection yoke 36 are controlled to direct the electron beam to a. desire si i On h Screen 11 Adjustment of the beam cross section as it asses through the apertures 14 is accomplished by appropriate adjustment of the potential V5. lf the cylinders 24 and 27 are connected to each other and thus operate at the same potential (i.e.. V4 equals VS) a symmetrical Einzel lens results from the cylinders M, 26 and 27. This aids in accomplishing satisfactory trimming of the beam. Adjustment of the voltages V4 and V is made until the cross section of the beam impinging upon th plate 13 isof adesired' size.

when a shaped beam tube of the type described is used without the item 18, described in detail below, a pronounced variation in intensity across the cross section of the trimmed beam results. A typical variation in such intensity is illustrated in FIG. 2 by the curve 37. lt may be seen that the region of uniform brightness of the electron beam under such circumstances is quite narrow. To achieve a reasonable degree of uniformity and brightness for a'character produced by one of the apertures 14, the total beam cross section at the plate i3 must be made relatively large so that only the region of uniform brightness floods the aperture. Since the lower intensity fringes of the beam cover a substantial area. as indicated by the dotted line 38 surrounding the aperture T in H6. 3, the adjacent apertures must be spaced a sufficient distance so as to be not included in this perimeter. For a given available area. such being typically limited by practical considerations of tube neck diameter and lens diameter, the number of apertures which may be utilized is accordingly limited ln accordance with the invention. the capacity oi a given area for containing shaping apertures is substantially increased by providing the mesh or grid 18 adjacent to the trim aperture 17. ln the preferred embodiment, the grid or mesh id is contained within an annular support 39 which is disposed flush against the plate 16. although shown'spaced apart from the plate 16 in FIG. 1 for clarity of illustration. The mesh is electrically conductive, as is its annular support 39, and is thus maintained at the same potential as the cylinder 26 and the plate 16 in a field-free region within the cylinder. The fineness and transmission capacity of the mesh is selected to cause a difiusion of the beam. It is believed that such diffusion results from the mesh causing a separation of the beam into a large number of separate small beams. each of which spreads as a result of space charge effects. Preferably, the mesh has about 500 lines per inch and about 60 percent open area, to permit transmission of 60 percent of the incident beam. A satisfactory mesh may be made by photoetching thin nickel sheets.

The effect of the mesh is illustrated by the curve 41 in FIG. 2. it may be seen that, although a lower peak intensity results, a spread in intensity also occurs. making the region of uniform intensity with the mesh present substantially wider than the region of uniform intensity without utilization of the mesh. Since the region of uniform intensity is substantially greater in the shaped beam tube of the invention, the potentials V4 and V5 may be adjusted so that the size of the beam cross section at the apertured plate 13 is substantially less than in the situation described in connection with FIG. 3. This is illustrated in FlG. 4, wherein the dotted square 42 represents the outer periphery of the electron beam at the plate 13 which is required under conditions of a large region of uniform intensity. it may be seen that this region is smaller than in FIG. 37 Accordingly, the apertures 14 may be spaced much closer to each other, enabling use ofa larger number of apertures for a given available area. Moreover, the uniformity of brightness in the character when displayed upon the cathode ray tube screen is superior to that of a shaped beam tube not constructed in ac cordance with the invention.

The lenses formed by the cylinders 32. 52, and 62 are constructed to sharply image the plane of the shaping aperture plate 13 on the target screen. The potentials of the cylinders 24 and 27 are adjusted so that the plane of the the trim aperture i7 is not imaged in the plane of the shaping apertures 14. Accordingly, there is no sharp reproduction of the mesh 18 on the target screen. Such focusing is controlled by the potentials V1-V5. The electrostatic lenses at element 27, formed by the discontinuity of potential between the cylinder 27 and the cylinders 26 and 28 serve only to control the beam cross-sectional size.

It may therefore be seen that the invention provides an improved shaped beam tube in which a larger number of shaping apertures may be incorporated for a given available area and in which superior quality ofimage brightness is attained. Various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims.

lclaim:

l. A shaped beam tube comprising:

an electron gun for producing a beam of electrons,

a target screen,

beam shaping means defining a plurality of shaping apertures positioned between said electron gun and said target screen for forming the cross section of the electron beam into a predetermined shape corresponding to the shape of the particular shaping aperture through which the beam is directed,

beam trimming means defining a substantially rectangular trim aperture positioned between said electron gun and said beam shaping means for reducing and generally shaping the cross section of the beam prior to its passing through said beam shaping means in a manner leaving \ni-sikh'iiiiili'i nnlv sufficient o erall cro section to satisfactorily illuminate the beam shaping apertures of said beam shaping means,

a mesh disposed closely adjacent said beam trimming means and positioned to act on said electron beam prior to its passing through said beam shaping means,

said mesh and said beam trimming means being both disposed in a hollow conductive member assuring a fieldfree region about said mesh and said beam trimming means,

said mesh being of a fineness and transmission capacity to effect substantial diffusion of the beam to produce a substantially uniform intensity over the cross section of the beam passing through the particular shaping aperture to which the beam is directed,

whereby said plurality of shaping apertures may be spaced relatively close to each other without illumination by the beam of shaping apertures adjacent said particular aperture, while obtaining uniformity of brightness of said predetermined shape on said target screen.

2. A shaped beam tube according to claim 1 including electron lens means for imaging the plane of said beam shaping means near the plane of said target screen. and for imaging said mesh in a plane substantially displaced from said beam shaping means along the beam axis.

3. A shaped beam tube according to claim 1 including elec tron lens means for providing a beam cross section nodal point near the plane ofsaid particular shaping aperture. 4. A shaped beam tube according to claim 1 wherein mesh is constructed to provide of the order of 500 lines per inch width of the order of 60 percent transmission.

5. A shaped beam tube according to claim 2 wherein said electron lens means include a first electrostatic lens for imaging the plane of said beam shaping means near the plane of said target screen. and a second electrostatic lens for imaging said mesh in a plane substantially displaced along the beam axis from said beam shaping member. 

1. A shaped beam tube comprising: an electron gun for producing a beam of electrons, a target screen, beam shaping means defining a plurality of shaping apertures positioned between said electron gun and said target screen for forming the cross section of the electron beam into a predetermined shape corresponding to the shape of the particular shaping aperture through which the beam is directed, beam trimming means defining a substantially rectangular trim aperture positioned between said electron gun and said beam shaping means for reducing and generally shaping the cross section of the beam prior to its passing through said beam shaping means in a manner leaving substantially only sufficient overall beam cross section to satisfactorily illuminate the beam shaping apertures of said beam shaping means, a mesh disposed closely Adjacent said beam trimming means and positioned to act on said electron beam prior to its passing through said beam shaping means, said mesh and said beam trimming means being both disposed in a hollow conductive member assuring a field-free region about said mesh and said beam trimming means, said mesh being of a fineness and transmission capacity to effect substantial diffusion of the beam to produce a substantially uniform intensity over the cross section of the beam passing through the particular shaping aperture to which the beam is directed, whereby said plurality of shaping apertures may be spaced relatively close to each other without illumination by the beam of shaping apertures adjacent said particular aperture, while obtaining uniformity of brightness of said predetermined shape on said target screen.
 2. A shaped beam tube according to claim 1 including electron lens means for imaging the plane of said beam shaping means near the plane of said target screen, and for imaging said mesh in a plane substantially displaced from said beam shaping means along the beam axis.
 3. A shaped beam tube according to claim 1 including electron lens means for providing a beam cross section nodal point near the plane of said particular shaping aperture.
 4. A shaped beam tube according to claim 1 wherein said mesh is constructed to provide of the order of 500 lines per inch width of the order of 60 percent transmission.
 5. A shaped beam tube according to claim 2 wherein said electron lens means include a first electrostatic lens for imaging the plane of said beam shaping means near the plane of said target screen, and a second electrostatic lens for imaging said mesh in a plane substantially displaced along the beam axis from said beam shaping member. 